U.S. patent number 10,848,262 [Application Number 16/336,160] was granted by the patent office on 2020-11-24 for optical path design apparatus and optical path design method.
This patent grant is currently assigned to NEC CORPORATION. The grantee listed for this patent is NEC Corporation. Invention is credited to Shinsuke Fujisawa, Akio Tajima, Hitoshi Takeshita.
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United States Patent |
10,848,262 |
Takeshita , et al. |
November 24, 2020 |
Optical path design apparatus and optical path design method
Abstract
In an optical communication network using the wavelength
division multiplexing system, the accommodation efficiency for the
optical paths decreases, and it becomes difficult to use the
optical communication network efficiently, if the optical frequency
slots are used concentrically in a specific optical fiber;
therefore, an optical path design apparatus according to an
exemplary aspect of the present invention includes route candidate
selection means for searching for a route of an optical path to
accommodate a communication demand and selecting a plurality of
route candidates; optical path candidate selection means for
selecting a plurality of optical path candidates by allocating an
optical frequency band required to accommodate the optical path to
each of optical fibers on the plurality of route candidates; and
optical path determination means for determining the optical path
from among the plurality of optical path candidates based on an
optical frequency band utilization rate in the optical fibers.
Inventors: |
Takeshita; Hitoshi (Tokyo,
JP), Fujisawa; Shinsuke (Tokyo, JP),
Tajima; Akio (Tokyo, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
NEC Corporation |
Tokyo |
N/A |
JP |
|
|
Assignee: |
NEC CORPORATION (Tokyo,
JP)
|
Family
ID: |
1000005204739 |
Appl.
No.: |
16/336,160 |
Filed: |
September 20, 2017 |
PCT
Filed: |
September 20, 2017 |
PCT No.: |
PCT/JP2017/033815 |
371(c)(1),(2),(4) Date: |
March 25, 2019 |
PCT
Pub. No.: |
WO2018/056285 |
PCT
Pub. Date: |
March 29, 2018 |
Prior Publication Data
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|
|
|
Document
Identifier |
Publication Date |
|
US 20190260474 A1 |
Aug 22, 2019 |
|
Foreign Application Priority Data
|
|
|
|
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Sep 26, 2016 [JP] |
|
|
2016-186852 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J
14/0267 (20130101) |
Current International
Class: |
H04J
14/02 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
2003-009194 |
|
Jan 2003 |
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JP |
|
2008-245225 |
|
Oct 2008 |
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JP |
|
2011-176631 |
|
Sep 2011 |
|
JP |
|
2016-111599 |
|
Jun 2016 |
|
JP |
|
2012/057095 |
|
May 2012 |
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WO |
|
2016/047101 |
|
Mar 2016 |
|
WO |
|
Other References
Written Opinion of the International Searching Authority of
PCT/JP2017/033815 dated Dec. 19, 2017. cited by applicant .
International Search Report of PCT/JP2017/033815 dated Dec. 19,
2017. cited by applicant.
|
Primary Examiner: Kretzer; Casey L
Attorney, Agent or Firm: Sughrue Mion, PLLC
Claims
The invention claimed is:
1. An optical path design apparatus, comprising: a route candidate
selection section configured to search for a route of an optical
path to accommodate a communication demand and to select a
plurality of route candidates; an optical path candidate selection
section configured to select a plurality of optical path candidates
by allocating an optical frequency band required to accommodate the
optical path to each of optical fibers on the plurality of route
candidates; and an optical path determination section configured to
determine the optical path from among the plurality of optical path
candidates based on an optical frequency band utilization rate in
the optical fibers, wherein the optical path determination section
determines, as the optical path, the optical path candidate with a
minimum optical frequency band utilization rate in a maximum
accommodation optical fiber in which the optical frequency band
utilization rate is a maximum among the optical fibers on the
plurality of route candidates.
2. The optical path design apparatus according to claim 1, wherein
the route candidate selection section selects the plurality of
route candidates based on optical transmission performance using
the optical fibers.
3. The optical path design apparatus according to claim 2, wherein
the optical path determination section selects, among the optical
fibers, an additional optical path using an optical fiber with the
optical frequency band utilization rate being less than a
predetermined value, determines an additional optical fiber to
accommodate the additional optical path, and determines the
additional optical path as the optical path.
4. The optical path design apparatus according to claim 2, wherein
the optical transmission performance includes at least one of an
optical signal-to-noise ratio, a nonlinear effect of an optical
fiber, a crosstalk between adjacent wavelength channels, and a
passband narrowing effect due to an optical band pass filter.
5. The optical path design apparatus according to claim 1, wherein
the optical path determination section selects, among the optical
fibers, an additional optical path using an optical fiber with the
optical frequency band utilization rate being less than a
predetermined value, determines an additional optical fiber to
accommodate the additional optical path, and determines the
additional optical path as the optical path.
6. The optical path design apparatus according to claim 1, further
comprising a warning section configured to calculate, before
determining the optical path, the optical frequency band
utilization rate in the optical fibers and generate warning
information when the optical frequency band utilization rate having
been calculated exceeds a predetermined threshold value.
7. The optical path design apparatus according to claim 1, wherein
the optical frequency band utilization rate is calculated by using
at least one of number of optical frequency slots, number of
optical paths, and number of optical frequency slots that are
continuously arranged.
8. An optical path design method, comprising: searching for a route
of an optical path to accommodate a communication demand and
selecting a plurality of route candidates; selecting a plurality of
optical path candidates by allocating an optical frequency band
required to accommodate the optical path to each of optical fibers
on the plurality of route candidates; and determining the optical
path from among the plurality of optical path candidates based on
an optical frequency band utilization rate in the optical fibers,
wherein the determining of the optical path includes determining,
as the optical path, the optical path candidate with a minimum
optical frequency band utilization rate in a maximum accommodation
optical fiber in which the optical frequency band utilization rate
is a maximum among the optical fibers on the plurality of route
candidates.
9. The optical path design method according to claim 8, wherein the
determining of the optical path includes selecting, among the
optical fibers, an additional optical path using an optical fiber
with the optical frequency band utilization rate being less than a
predetermined value, determining an additional optical fiber to
accommodate the additional optical path, and determining the
additional optical path as the optical path.
10. The optical path design method according to claim 8, wherein
the selecting of the plurality of route candidates includes
selecting the plurality of route candidates based on optical
transmission performance using the optical fibers.
11. The optical path design method according to claim 10, wherein
the optical transmission performance includes at least one of an
optical signal-to-noise ratio, a nonlinear effect of an optical
fiber, a crosstalk between adjacent wavelength channels, and a
passband narrowing effect due to an optical band pass filter.
12. The optical path design method according to claim 8, wherein
the optical frequency band utilization rate is calculated by using
at least one of number of optical frequency slots, number of
optical paths, and number of optical frequency slots that are
continuously arranged.
13. An optical path design method, comprising: searching for a
route of an optical path to accommodate a communication demand and
selecting a plurality of route candidates; selecting a plurality of
optical path candidates by allocating an optical frequency band
required to accommodate the optical path to each of optical fibers
on the plurality of route candidates; determining the optical path
from among the plurality of optical path candidates based on an
optical frequency band utilization rate in the optical fibers; and
calculating, before determining the optical path, the optical
frequency band utilization rate in the optical fibers and
generating warning information when the optical frequency band
utilization rate having been calculated exceeds a predetermined
threshold value.
14. An optical path design apparatus, comprising: a route candidate
selection section configured to search for a route of an optical
path to accommodate a communication demand and select a plurality
of route candidates; an optical path candidate selection section
configured to select a plurality of optical path candidates by
allocating an optical frequency band required to accommodate the
optical path to each of optical fibers on the plurality of route
candidates; an optical path determination section configured to
determine the optical path from among the plurality of optical path
candidates based on an optical frequency band utilization rate in
the optical fibers; and a warning section configured to calculate,
before determining the optical path, the optical frequency band
utilization rate in the optical fibers and generate warning
information when the optical frequency band utilization rate having
been calculated exceeds a predetermined threshold value, wherein
the route candidate selection section selects the plurality of
route candidates based on an optical transmission performance using
the optical fibers.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a National Stage of International Application
No. PCT/JP2017/033815 filed Sep. 20, 2017, claiming priority based
on Japanese Patent Application No. 2016-186852 filed Sep. 26, 2016,
the disclosure of which are incorporated herein in their entirety
by reference.
TECHNICAL FIELD
The present invention relates to optical path design apparatuses
and optical path design methods and, in particular, to an optical
path design apparatus and an optical path design method that are
used in an optical communication network according to a wavelength
division multiplexing system.
BACKGROUND ART
A communication capacity in a core network is required to be
expanded due to explosive spread of mobile terminals, rapid
expansion of high-definition video distribution services, and the
like. Such a requirement to expand the capacity tends to continue
in the future. In order to continuously expand the communication
capacity at limited cost, it is effective to increase utilization
efficiency of the network by efficiently operating resources of the
network.
Particularly, in an optical communication network in which an
information capacity to be handled is extremely large, it is
important to efficiently use an optical frequency band of
communication resources. When the optical frequency band is used in
the optical communication network, it is necessary to consider a
quality degradation of an optical signal that is caused by
restrictions due to a variety of physical laws in optical signal
transmission. The physical restrictions in this case include, for
example, a crosstalk between adjacent wavelength channels in
wavelength multiplexing optical signal transmission, a degradation
of an optical signal/noise (S/N) ratio that is caused by an optical
fiber loss or an optical noise added by an optical amplifier, and
the like. In addition, a passband narrowing effect caused by
passing through a plurality of optical band pass filters (BPFs) is
also included in the above-mentioned physical restrictions.
In the optical communication network, as a transmission distance of
the optical signal from a communication source to a communication
destination, that is, an optical path length is shorter,
communication with better quality becomes possible because of a
small effect of the physical restrictions as described above.
Hence, when there are a plurality of options in a route from the
communication source to the communication destination, a shortest
route is selected. The Dijkstra's algorithm is often used for
searching for the shortest route. An optical frequency band is
allocated on the selected shortest route.
Meanwhile, an optical communication network utilizing a flexible
grid (a flexible optical network) can raise optical frequency
utilization efficiency, even though a communication capacity is
unchanged, by increasing or decreasing a required optical frequency
band depending on a transmission distance. This is an excellent
feature in comparison with a fixed grid that has been
conventionally used. The required optical frequency band requires a
wider band as the transmission distance becomes longer;
accordingly, a shorter transmission distance has more advantage in
the optical frequency utilization efficiency.
Patent Literature 1 discloses an example of a frequency/route
determination apparatus to allocate a frequency with a variable
width in the above-described flexible optical network. The
route/frequency determination apparatus in Patent Literature 1
includes a resource information DB, a common free frequency
information generation unit, a frequency state evaluation unit, a
frequency/route determination unit, and a communication route
demand distribution DB.
The common free frequency information generation unit obtains
resource information of a plurality of fibers that are calculation
targets from the resource information DB, and generates free
frequency information common to the obtained fibers. The frequency
state evaluation unit provides an evaluation value in consideration
of consecutiveness of free frequency on free resource information,
and in consideration of distribution of assumed communication
routes for the assumed communication route setting request.
The frequency/route determination unit calculates a candidate route
and a frequency that becomes an assignment candidate. The
frequency/route determination unit calculates a metric based on the
evaluation value given by the frequency state evaluation unit, the
metric being a value for calculating a determined candidate from a
plurality of candidates of combinations of candidate routes and
assigned frequency. The frequency/route determination unit
calculates an optimum route and assigning frequency based on the
calculated metric.
It is said that those configurations make it possible to
effectively suppress occurrence of fragmentation in the flexible
optical network, and to optimize utilization efficiency of
frequency resources.
CITATION LIST
Patent Literature
PTL 1: WO 2012/057095
SUMMARY OF INVENTION
Technical Problem
In optical path design in an optical communication network, it is
important to search for many optical paths under the condition that
communication resources are constant. In case of failure to search
for an optical path to a desired communication demand, it is
necessary to additionally provide communication resources such as
optical fibers and transponders in order to open the optical path.
However, it is undesirable to provide the communication resources
additionally because an additional cost is generated. Consequently,
it is important to perform optical path design to succeed in
searching for many optical paths without providing the
communication resource additionally. That is to say, accommodation
efficiency for optical paths increases as the number of optical
paths succeeding in the search becomes larger; accordingly, it
becomes possible to utilize the optical communication network
efficiently.
As mentioned above, Patent Literature 1 discloses the
route/frequency determination apparatus that makes it possible to
effectively suppress the occurrence of fragmentation of optical
frequency slots and maximize the utilization efficiency of optical
frequency resources. However, if the occurrence of the
fragmentation of optical frequency slots is suppressed, the optical
frequency slots are used concentrically in a specific optical
fiber; accordingly, it becomes difficult to set an optical path
passing through the specific optical fiber. As a result, the
accommodation efficiency for the optical paths decreases, and
efficient use of the optical communication network is
prevented.
As described above, there has been the problem that, in an optical
communication network using the wavelength division multiplexing
system, the accommodation efficiency for the optical paths
decreases, and it becomes difficult to use the optical
communication network efficiently, if the optical frequency slots
are used concentrically in a specific optical fiber.
The object of the present invention is to provide an optical path
design apparatus and an optical path design method that solve the
above-mentioned problem that, in an optical communication network
using the wavelength division multiplexing system, the
accommodation efficiency for the optical paths decreases, and it
becomes difficult to use the optical communication network
efficiently, if the optical frequency slots are used concentrically
in a specific optical fiber.
Solution to Problem
An optical path design apparatus according to an exemplary aspect
of the present invention includes route candidate selection means
for searching for a route of an optical path to accommodate a
communication demand and selecting a plurality of route candidates;
optical path candidate selection means for selecting a plurality of
optical path candidates by allocating an optical frequency band
required to accommodate the optical path to each of optical fibers
on the plurality of route candidates; and optical path
determination means for determining the optical path from among the
plurality of optical path candidates based on an optical frequency
band utilization rate in the optical fibers.
An optical path design method according to an exemplary aspect of
the present invention includes searching for a route of an optical
path to accommodate a communication demand and selecting a
plurality of route candidates; selecting a plurality of optical
path candidates by allocating an optical frequency band required to
accommodate the optical path to each of optical fibers on the
plurality of route candidates; and determining the optical path
from among the plurality of optical path candidates based on an
optical frequency band utilization rate in the optical fibers.
Advantageous Effects of Invention
According to an optical path design apparatus and an optical path
design method of the present invention, it becomes possible, in an
optical communication network using a wavelength division
multiplexing system, to increase the accommodation efficiency for
optical paths and to use the optical communication network
efficiently.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a block diagram illustrating a configuration of an
optical path design apparatus according to a first example
embodiment of the present invention.
FIG. 2 is a diagram schematically illustrating a configuration of
an optical communication network to explain the operation of the
optical path design apparatus according to the first example
embodiment of the present invention.
FIG. 3 is a diagram illustrating reachability of an optical signal
in the optical communication network according to the first example
embodiment of the present invention.
FIG. 4 is a diagram illustrating utilization situations of optical
frequency slots in respective optical fibers in the optical
communication network according to the first example embodiment of
the present invention.
FIG. 5 is a diagram illustrating utilization situations of the
optical frequency slots in the optical fibers when an optical path
to accommodate a new demand is searched based on a related
method.
FIG. 6 is a flowchart to explain the operations of the optical path
design apparatus according to the first example embodiment of the
present invention.
FIG. 7 is a diagram illustrating utilization situations of the
optical frequency slots when the optical path design apparatus
according to the first example embodiment of the present invention
sets a new optical path.
FIG. 8 is a block diagram illustrating a configuration of an
optical node apparatus according to the first example embodiment of
the present invention.
FIG. 9 is a flowchart to explain the operations of an optical path
design apparatus according to a second example embodiment of the
present invention.
FIG. 10 is a diagram illustrating search situations for optical
paths, for explaining the operations of the optical path design
apparatus according to the second example embodiment of the present
invention.
FIG. 11 is a diagram illustrating utilization situations of optical
frequency slots in optical fibers corresponding to a new optical
path that is searched for by the optical path design apparatus
according to the second example embodiment of the present
invention.
FIG. 12 is a diagram illustrating utilization situations of the
optical frequency slots in the optical fibers corresponding to the
new optical path that is searched for by the optical path design
apparatus according to the second example embodiment of the present
invention.
FIG. 13 is a block diagram illustrating a configuration of an
optical path design apparatus according to a third example
embodiment of the present invention.
FIG. 14 is a flowchart to explain the operations of the optical
path design apparatus according to the third example embodiment of
the present invention.
EXAMPLE EMBODIMENT
Example embodiments of the present invention will be described
below with reference to the drawings.
First Example Embodiment
FIG. 1 is a block diagram illustrating a configuration of an
optical path design apparatus 100 according to a first example
embodiment of the present invention.
The optical path design apparatus 100 includes a route candidate
selection section (route candidate selection means) 110, an optical
path candidate selection section (optical path candidate selection
means) 120, and an optical path determination section (optical path
determination means) 130.
The route candidate selection section 110 searches for a route of
an optical path to accommodate a communication demand, and selects
a plurality of route candidates. The optical path candidate
selection section 120 selects a plurality of optical path
candidates by allocating an optical frequency band required to
accommodate the optical path to each of optical fibers on the
plurality of route candidates. The optical path determination
section 130 determines the optical path to accommodate the
communication demand from among the plurality of optical path
candidates based on an optical frequency band utilization rate in
the optical fibers.
As described above, the optical path design apparatus 100 according
to the present example embodiment is configured to determine an
optical path, from among a plurality of optical path candidates
differing from each other in a route, based on the optical
frequency band utilization rate in the optical fiber on the route.
This makes it possible to prevent a decrease in the accommodation
efficiency for optical paths that is caused by selecting a route in
which there is no unused optical frequency band. As a result,
according to the optical path design apparatus 100 of the present
example embodiment, it becomes possible, in an optical
communication network using a wavelength division multiplexing
system, to increase the accommodation efficiency for the optical
paths and to use the optical communication network efficiently.
The route candidate selection section 110 can be configured to
select the plurality of route candidates based on optical
transmission performance using the optical fiber on the route. In
other words, the route candidate selection section 110 can be
configured to determine whether or not an optical signal is
reachable based on the optical transmission performance and to
select, as a route candidate, only the route that is determined to
be reachable. Here, the optical transmission performance includes
at least one of an optical signal-to-noise ratio, a nonlinear
effect of optical fibers, a crosstalk between adjacent wavelength
channels, and a passband narrowing effect due to an optical band
pass filter.
The optical path determination section 130 can be configured to
determine, as the optical path to accommodate the communication
demand, an optical path candidate with minimum optical frequency
band utilization rate in a maximum accommodation optical fiber in
which an optical frequency band utilization rate is maximum among
the optical fibers on the route. The optical frequency band
utilization rate can be calculated by using at least one of the
number of optical frequency slots, the number of optical paths, and
the number of optical frequency slots that are continuously
arranged.
Next, the operation of the optical path design apparatus 100
according to the present example embodiment will be described in
detail. Hereinafter, the operation will be described by taking, as
an example, an optical communication network 1000 composed of 16
nodes illustrated in FIG. 2. In FIG. 2, respective circles
represent respective optical nodes 1001 to 1016. The respective
optical nodes 1001 to 1016 are connected to one another by optical
fibers composed of twelve optical fibers 1201 to 1212 that connect
the respective optical nodes to one another in a lateral direction
in FIG. 2 and twelve optical fibers 1301 to 1312 that connect the
respective optical nodes to one another in a longitudinal direction
in FIG. 2.
As illustrated in FIG. 2, an optical path 1101 and an optical path
1102 are set in the optical communication network 1000. The optical
path 1101 accommodates a communication demand ranging from the
optical node 1001 to the optical node 1010. The optical path 1102
accommodates a demand ranging from the optical node 1003 to the
optical node 1010. It is assumed that relationships illustrated in
FIG. 3 are known in advance about the reachability of an optical
signal, with regard to the optical communication network 1000.
Here, in the optical communication network 1000, each distance
between all optical nodes is set to be equal. Consequently, a
length of an optical path connecting the optical node to one
another, that is, a distance over which the optical signal should
reach, is proportional to the number of hops between the optical
nodes. Because the optical communication network 1000 is a flexible
optical network utilizing a flexible grid, the optical frequency
band is allocated to the optical path by the optical frequency slot
with 12.5 GHz serving as a unit, for example. FIG. 3 illustrates a
relationship, where the optical signal reaches throughout desired
number of hops, between the number of hops and the number of
optical frequency slots needed for that case. That is to say, FIG.
3 shows a necessary optical frequency band for the optical signal
to reach to a desired distance.
For example, when the number of hops in the optical path is two,
FIG. 3 shows that the required number of optical frequency slots is
one. When the number of hops exceeds six, FIG. 3 shows that it is
impossible for the optical signal to reach due to restrictions of
the performance of a transponder that transmits and receives the
optical signal, even though the number of optical frequency slots
is made larger than ten. Each of the optical fibers 1201 to 1212
and 1301 to 1312 is assumed to have a capacity enough to
accommodate six optical frequency slots.
FIG. 4 illustrates utilization situations of the optical frequency
slots in the optical fibers 1306, 1307 and 1308 in situations where
the optical path 1101 and the optical path 1102 are set as
illustrated in FIG. 2.
In this case, a utilization rate .eta. of the optical frequency
slots in the optical fiber 1306 can be calculated as 4/6=0.67. When
utilization rates of the optical frequency slots in the other
optical fibers 1307 and 1308 are calculated in the same manner,
both calculated results become 0. Accordingly, it is in the optical
fiber 1306 that an optical frequency slot utilization rate is
maximized, in the optical path setting situations of the optical
communication network 1000 illustrated in FIG. 2. The optical
frequency slot utilization rate .eta. in this time becomes 4/6.
A case will be described where a demand from the optical node 1005
to the optical node 1010 newly occurs. It is assumed that the
setting of an optical path passing through the optical node 1009 is
inhibited. First, a search for the optical path based on a related
method will be described as a comparative example. In the related
method, a route is searched for in which a route length from the
optical node 1005 to the optical node 1010 becomes shortest.
Accordingly, an optical path 1103 is obtained in which the number
of hops is two (see FIG. 2). FIG. 3 shows that the number of
required optical frequency slots is one when the number of hops is
two. Consequently, the utilization situations of the optical
frequency slots in this case become those illustrated in FIG. 5. As
is the case with those illustrated in FIG. 4, an optical frequency
slot utilization rate .eta. in the optical fiber in which the
optical frequency slot utilization rate becomes maximum (optical
fiber 1306) is calculated to be 5/6.
Next, a search for an optical path according to the optical path
design apparatus 100 of the present example embodiment will be
described in detail. The optical path design apparatus 100
according to the present example embodiment sets priority for each
of the route length and the optical frequency slot utilization
rate. A decision based on the optical frequency slot utilization
rate has priority over a decision based on the route length. Here,
a case will be described with reference to FIG. 6 where higher
priority is set to the route length as the route length is shorter,
and higher priority is set to the optical frequency slot
utilization rate as the optical frequency slot utilization rate is
lower.
FIG. 6 is a flowchart to explain the operations of the optical path
design apparatus 100 according to the present example
embodiment.
When a demand occurs (Step S3001), first, a route search for an
optical path accommodating the demand is performed (Step S3002).
When the route search results in failure (Step S3002/NO), a desired
optical path cannot be opened.
When the route search results in success (Step S3002/YES), the
number of optical frequency slots required to open an optical path
using the route is calculated (Step S3003). After the number of
required optical frequency slots is determined, the optical
frequency slots are allocated to respective optical fibers on the
searched route (Step S3007). When there are unallocated optical
frequency slots of which number is equal to or more than the number
of optical frequency slots determined in Step S3003 in all the
optical fibers on the route, the allocation results in success
(Step S3007/YES).
When the allocation results in failure because there is a shortage
of the unallocated optical frequency slots in the optical fiber
(Step S3007/NO), and the number of allocation failure times is
lower than a predetermined maximum number of times N of the route
search, the route search is redone (Step S3005/YES). However, in
this case, the search is performed excepting routes for which the
allocation of the optical frequency slots results in failure. When
the allocation of the optical frequency slots does not result in
success by the number of redoing times that is lower than the
maximum number of times N of the route search, the optical path
search is regarded as a failure.
When the allocation of the optical frequency slots results in
success (Step S3007/YES), the result is stored as an optical path
candidate in the path candidate database (DB) together with the
optical frequency slot utilization situations of the respective
optical fibers (Step S3004).
The sequence of operations mentioned above are repeated until the
number of times exceeds the maximum number of times N of the route
search.
When the number k of path candidates stored in the path candidate
database is equal to zero (Step S3009/NO), the optical path search
is regarded as a failure.
When the number k of the path candidates is larger than zero (Step
S3009/YES), there is at least one optical path that can accommodate
the demand having occurred in Step S3001. When there are a
plurality of optical path candidates, an optical frequency slot
utilization rate .eta. is calculated for each of the plurality of
optical path candidates (Step S3006). Then an optical path for
which the optical frequency slot utilization rate .eta. becomes
minimum is extracted from the optical path candidates (Step S3008),
and the extracted optical path is determined to be an optical path
that accommodates the demand occurred. These steps make the optical
path search successful.
Taking for example the above-mentioned case where the demand from
the optical node 1005 to the optical node 1010 newly occurs, the
optical path design apparatus 100 first searches for a route
ranging from the optical node 1005 to the optical node 1010 (Step
S3002). In this case also, the shortest route is optical path 1103
as is the case with the related method.
Other routes, which are not the shortest route, ranging from the
optical node 1005 to the optical node 1010 can also be detected.
One of the other routes is an optical path 1104 with the number of
hops equal to four. The optical path 1104 is a route ranging from
the optical node 1005 to the optical node 1010, and is a shortest
route among routes with the number of hops larger than two. The
number of optical frequency slots required to open the optical path
1104 is calculated to be two from FIG. 3 (Step S3003). Because
there is more than one unallocated optical frequency slot in the
optical fiber 1307 as illustrated in FIG. 4, the optical path 1104
is made a success in allocating the optical frequency slots (Step
S3007).
An optical path with the shortest route length next to the optical
path 1104 is an optical path 1105 (see FIG. 2). Because the number
of hops in the optical path 1105 is six, the number of required
optical frequency slots is calculated to be 10 from FIG. 3 (Step
S3003). As mentioned above, it is assumed that each of the optical
fibers 1201 to 1212 and 1301 to 1312 has communication resources
that can accommodate up to six optical frequency slots.
Accordingly, the shortage of the communication resources makes it
impossible to open an optical path with regard to the optical path
1105 that requires ten optical frequency slots (Step S3007/NO).
FIG. 7 illustrates utilization situations of the optical frequency
slots when the optical path design apparatus 100 according to the
present example embodiment sets the optical path 1104.
The optical path design apparatus 100 stores the optical path 1104
in the path candidate database together with the optical frequency
slot utilization situation illustrated in FIG. 7 (Step S3004). A
similar procedure is also performed for path candidates other than
the optical path 1104, and the path candidate database is updated.
The above-described operations are repeated until the number of
times exceeds the predetermined maximum number of times N of the
route search. Because the optical path 1103 of a search result of
the optical path according to the related method can also be one of
the path candidates; accordingly, the optical path 1103 is also
stored in the path candidate data. Consequently, there is at least
one optical path candidate stored in the path candidate database;
therefore, it is ensured that the path search does not result in
failure (Step S3009/YES).
With regard to the utilization situations of the optical frequency
slots in the optical fibers on the route, the utilization situation
for the optical path 1103 is illustrated in FIG. 5, and the
utilization situation for the optical path 1104 is illustrated in
FIG. 7. It can be seen from FIG. 5 and FIG. 7 that it is the
optical fiber 1306 that the optical frequency slot utilization rate
becomes maximum for both of the optical path 1103 and the optical
path 1104. The optical frequency slot utilization rate .eta. in the
optical fiber 1306 is calculated as follows: .eta.=5/6 with regard
to the optical path 1103, and .eta.=4/6 with regard to optical path
1104 (Step S3006). With regard to path candidates other than the
optical paths 1103 and 1104, the optical frequency slot utilization
rate is calculated in a similar way. As a result, the optical path
1104 is extracted as an optical path for which the optical
frequency slot utilization rate .eta. in the optical fiber 1306
becomes minimum (Step S3008). This makes only one optical path
selected from among the plurality of path candidates, which leads
to a success in the optical path search.
Focusing attention on the number of unallocated optical frequency
slots in the optical fiber 1306, the number is one according to the
related method as can be seen from FIG. 5, whereas the number is
two according to the present example embodiment as can be seen from
FIG. 7. That is to say, the present example embodiment makes it
possible to increase the number of unallocated optical frequency
slots in the optical fiber 1306 more than one obtained by the
related method.
Here, another example will be considered in which the other new
demand occurs and the need arises to allocate two more optical
frequency slots to the optical fiber 1306. According to the related
method with the utilization situation of the optical frequency
slots illustrated in FIG. 5, a lack of the optical frequency slots
makes it impossible to open an optical path to accommodate the
demand. In contrast, according to the present example embodiment
with the utilization situation of the optical frequency slots
illustrated in FIG. 7, it is possible to open an optical path to
accommodate the demand because of no lack of the optical frequency
slots.
As described above, according to the optical path design apparatus
100 of the present example embodiment, it becomes possible to
prevent the allocated optical frequency slots from locally
concentrating on a specific optical fiber. As a result, it is
possible to improve a success rate in opening an optical path
compared to one according to the related method under the condition
that the communication resources are constant.
Next, an optical node apparatus will be described that is used in
each of the optical nodes 1001 to 1016 constituting the optical
communication network 1000. FIG. 8 illustrates a configuration of
an optical node apparatus 200 according to the present example
embodiment.
The optical node apparatus 200 includes: an optical path
information receiving section (optical path information receiving
means) 210, a variable optical transponder 220, a switching section
(switching means) 230, and an optical node controller (optical node
control means) 240.
The optical path information receiving section 210 receives route
information and optical frequency band information concerning an
optical path that accommodates a communication demand and that is
determined by the optical path design apparatus 100. The variable
optical transponder 220 generates signal light by modulating an
optical carrier wave based on a client signal included in the
communication demand. The variable optical transponder 220 is
configured to vary a center frequency and an optical frequency
bandwidth of the signal light. The switching section 230 is
connected to one end of an optical fiber and changes an
input/output route by the optical path. The optical node controller
240 controls the switching section 230 based on the route
information and controls the variable optical transponder 220 based
on the optical frequency band information.
Next, an optical path design method according to the present
example embodiment will be described.
In the optical path design method according to the present example
embodiment, first, a route of an optical path to accommodate a
communication demand is searched for, and a plurality of route
candidates are selected. A plurality of optical path candidates are
selected by allocating an optical frequency band required to
accommodate the optical path to each of optical fibers on the
plurality of route candidates. Then the optical path to accommodate
the communication demand is determined from among the plurality of
optical path candidates based on an optical frequency band
utilization rate in the optical fiber.
The determining of the optical path can include determining, as the
optical path to accommodate the communication demand, the optical
path candidate with minimum optical frequency band utilization rate
in a maximum accommodation optical fiber in which the optical
frequency band utilization rate is maximum among the optical
fibers.
The above-mentioned each step may be performed by a computer. That
is to say, it is possible to use a program that allows a computer
to function as a route candidate selection means, an optical path
candidate selection means, and an optical path determination
means.
The route candidate selection means is to search for a route of an
optical path to accommodate a communication demand, and select a
plurality of route candidates. The optical path candidate selection
means is to select a plurality of optical path candidates by
allocating an optical frequency band required to accommodate the
optical path to each of optical fibers on the plurality of route
candidates. The optical path determination means is to determine
the optical path from among the plurality of optical path
candidates based on an optical frequency band utilization rate in
the optical fiber.
As described above, according to the optical path design apparatus
100, the optical node apparatus 200, the optical path design
method, and the program of the present example embodiment, it
becomes possible, in an optical communication network using a
wavelength division multiplexing system, to increase the
accommodation efficiency for optical paths. As a result, it becomes
possible to use the optical communication network efficiently.
Second Example Embodiment
Next, a second example embodiment of the present invention will be
described. The configuration of an optical path design apparatus
according to the present example embodiment is similar to that
according to the first example embodiment (see FIG. 1).
In the optical path design apparatus according to the present
example embodiment, the optical path determination section 130
selects, among optical fibers on a plurality of route candidates,
an additional optical path that uses a band-unused optical fiber
with an optical frequency band utilization rate being less than
one. The optical path determination section 130 is configured to
determine the addition of an additional optical fiber to
accommodate the additional optical path and determine the
additional optical path as an optical path to accommodate a
communication demand.
That is to say, when the search for the optical path results in
failure due to insufficient communication resources in the optical
communication network 1000, the optical path design apparatus is
configured to avoid the failure in the optical path search by
adding required communication resources and calculate communication
resources required to accommodate all desired demands.
Next, the operation of the optical path design apparatus according
to the present example embodiment will be described more in detail
using FIG. 9. FIG. 9 is a flowchart to explain the operation of the
optical path design apparatus according to the present example
embodiment.
As illustrated in FIG. 9, the operation of the optical path design
apparatus according to the present example embodiment differs from
the operation of the optical path design apparatus according to the
first example embodiment (see FIG. 6) in that a step for adding an
optical fiber (Step S4010) is added. The other basic operations are
similar to the operations of the optical path design apparatus
according to the first example embodiment; accordingly, a different
operation will be described below in detail.
FIG. 10 illustrates search situations for optical paths, where an
optical path 6101 and an optical path 6102 are set in advance as
the initial state, and the demand from the optical node 1005 to the
optical node 1010 increases. FIG. 10 illustrates an example in
which optical paths 6103 to 6109 are searched for as additional
optical paths. FIG. 11 and FIG. 12 illustrate the utilization
situations of the optical frequency slots in the optical fiber
1306, the optical fiber 1307, and the optical fiber 1205, which
correspond to the optical paths in this case.
Starting from the initial state in which the optical path 6101 and
the optical path 6102 are set, optical paths to accommodate
increasing demands are added in accordance with the operation of
the optical path design apparatus of the present example embodiment
illustrated in FIG. 9.
First, it is an optical path 6103 that is an optical path to be set
when the demands are increased by one only. As illustrated in FIG.
10, the optical path 6103 starts from the optical node 1005, passes
through the optical fiber 1205 and the optical fiber 1307, and is
connected to the optical node 1010. The operation for setting the
optical path 6103 is as described in detail in the first example
embodiment.
FIG. 11 illustrates the utilization situations of the optical
frequency slots at this time. Because the optical path 6103 is an
optical path having four hops, the number of required optical
frequency slots is two according to FIG. 3. Consequently, two
optical frequency slots are allocated to each of the optical fibers
1205 and 1307 for the optical path 6103.
When the demands are further increased, the optical paths 6104 to
6106 are set in accordance with the operation of the optical path
design apparatus according to the present example embodiment
illustrated in FIG. 9. As a result, the utilization situations of
the optical frequency slots changes from the state illustrated in
FIG. 11 to the state illustrated in FIG. 12.
An example will be examined in which the demands are still further
increased. As can be seen from the utilization situations of the
optical frequency slots illustrated in FIG. 12, there is no unused
optical frequency slot in the optical fiber 1205 and the optical
fiber 1306. Accordingly, these optical fibers cannot be used. As a
result, an optical path 6108 bypassing these optical fibers becomes
a next candidate. However, because the number of hops in the
optical path 6108 is larger than six, the optical path 6108 cannot
be connected due to the restrictions on the reachability of the
optical signal illustrated in FIG. 3. Similar results are also
obtained for other optical path candidates; consequently, it is
determined that there is no connectable optical path whatever the
predetermined maximum number of times N of the route search may be
(Step S4009/NO in FIG. 9). Accordingly, the optical path design
apparatus according to the present example embodiment determines
that an optical fiber is added (Step S4010).
In adding an optical fiber (Step S4010), the optical fiber is added
so that the number of additional optical fibers may become minimum.
It can be seen from FIG. 12 that the optical fiber 1307 is an
optical fiber in which there is an unused optical frequency slot,
that is, a band-unused optical fiber with the optical frequency
band utilization rate being less than one. Consequently, it takes
priority to add an optical fiber prepared for an optical path
utilizing the optical fiber 1307. When the optical fiber 1307 is
used, it is optical path 6107 that can be opened. Because the
optical path 6107 also passes through the optical fiber 1205, the
optical path 6107 can be opened by adding one optical fiber of
optical fiber 6901 that connects the optical node 1105 and the
optical node 1106 as with the optical fiber 1205. Accordingly,
after determining the addition of the optical fiber 6901 (Step
S4010), the optical path design apparatus according to the present
example embodiment performs the route search once again (Step
S4002).
As described above, the addition of the optical fiber 6901 makes it
possible to open the optical path 6107 that has been unopenable due
to the shortage of the optical frequency slots. As a result, it is
possible to avoid the failure in the optical path search.
In the above-mentioned example, as illustrated in FIG. 10, one
optical fiber is disposed between respective optical nodes in the
initial state; accordingly, the total number of the optical fibers
is 24. From the initial state, one optical fiber of optical fiber
6901 is newly set up between the optical node 1005 and the optical
node 1006, which makes it possible to further open the optical path
6107.
The optical path design apparatus may be configured to hold the
addition of one optical fiber of optical fiber 6901 as the route
information in adding the optical fiber (Step S4010). This makes it
possible to know the number and the layout of the optical fibers
required to accommodate all desired demands.
As described above, according to the optical path design apparatus
and the optical path design method of the present example
embodiment, as is the case with the first example embodiment, it
becomes possible, in an optical communication network using a
wavelength division multiplexing system, to increase the
accommodation efficiency for optical paths. As a result, it becomes
possible to use the optical communication network efficiently.
Third Example Embodiment
Next, a third example embodiment of the present invention will be
described. FIG. 13 illustrates a configuration of an optical path
design apparatus 300 according to the present example
embodiment.
The optical path design apparatus 300 includes the route candidate
selection section (route candidate selection means) 110, the
optical path candidate selection section (optical path candidate
selection means) 120, and the optical path determination section
(optical path determination means) 130. The optical path design
apparatus 300 differs from the optical path design apparatus 100
according to the first example embodiment in that a warning section
(warning means) 340 is further included. The warning section 340
calculates an optical frequency band utilization rate in an optical
fiber and generates warning information when the calculated optical
frequency band utilization rate exceeds a predetermined threshold
value. The other configurations are similar to the configurations
of the optical path design apparatus 100 according to the first
example embodiment; accordingly, those descriptions will not be
repeated.
Next, the operation of the optical path design apparatus 300
according to the present example embodiment will be described. FIG.
14 illustrates a flowchart to explain the operations of the optical
path design apparatus 300 according to the present example
embodiment.
The optical path design apparatus 300 according to the present
example embodiment generates warning information when the optical
frequency slot utilization rate in the optical fiber exceeds a
predetermined threshold value th in the optical communication
network 1000. Then the optical path design apparatus 300 issues a
warning to a network management system and the like. The other
basic operations are similar to the operations of the optical path
design apparatus according to the first example embodiment;
accordingly, a different operation will be described below in
detail. When the utilization situations of the optical frequency
slots in the optical fibers changes to the states illustrated in
FIG. 12, there is no unallocated optical frequency slot in the
optical fiber 1306 and the optical fiber 1205. There is no route
that does not pass through the optical node 1009, does not use the
optical fiber 1306 and the optical fiber 1205, and can connect the
optical node 1005 and the optical node 1010 within six hops. This
makes it impossible due to insufficient communication resources,
even if a demand from the optical node 1005 to the optical node
1010 newly occurs, to generate a new optical path to accommodate
the demand. In order to avoid the above, it is only necessary to
add the communication resources such as an optical fiber. However,
it takes time to provide additional communication resources. The
optical path design apparatus 300 according to the present example
embodiment is configured to anticipate in advance a shortage of the
communication resources in the future and to prevent it from
arising that insufficient communication resources make it
impossible to generate an optical path.
In calculating the optical frequency slot utilization rate .eta.
(Step S5006 in FIG. 14), the optical path design apparatus 300
according to the present example embodiment understands the
utilization situations of the optical frequency slots in the
respective optical fibers that constitute the optical communication
network 1000. When the utilization rate of the optical frequency
slots exceeds the predetermined threshold value th (Step
S5010/YES), the optical path design apparatus 300 issues, to a
network management system that manages the entire network, a
warning to the effect that the communication resources are running
short, for example. Receiving the warning enables the network
management system to additionally provide the optical fiber for the
right place at the right time. This makes it possible to avoid the
situation that it becomes impossible to generate an optical path
due to insufficient communication resources.
In addition, according to the optical path design apparatus 300 and
the optical path design method of the present example embodiment,
as is the case with the first example embodiment, it becomes
possible, in an optical communication network using a wavelength
division multiplexing system, to increase the accommodation
efficiency for optical paths. As a result, it becomes possible to
use the optical communication network efficiently.
The whole or part of the example embodiments disclosed above can be
described as, but not limited to, the following supplementary
notes.
(Supplementary note 1) An optical path design apparatus,
comprising: route candidate selection means for searching for a
route of an optical path to accommodate a communication demand and
selecting a plurality of route candidates; optical path candidate
selection means for selecting a plurality of optical path
candidates by allocating an optical frequency band required to
accommodate the optical path to each of optical fibers on the
plurality of route candidates; and optical path determination means
for determining the optical path from among the plurality of
optical path candidates based on an optical frequency band
utilization rate in the optical fibers.
(Supplementary note 2) The optical path design apparatus according
to Supplementary note 1, wherein the route candidate selection
means selects the plurality of route candidates based on optical
transmission performance using the optical fibers.
(Supplementary note 3) The optical path design apparatus according
to Supplementary note 1 or 2, wherein the optical path
determination means determines, as the optical path, the optical
path candidate with minimum optical frequency band utilization rate
in a maximum accommodation optical fiber in which the optical
frequency band utilization rate is maximum among the optical
fibers.
(Supplementary note 4) The optical path design apparatus according
to any one of Supplementary notes 1, 2, and 3, wherein the optical
path determination means selects, among the optical fibers, an
additional optical path using a band-unused optical fiber with the
optical frequency band utilization rate being less than one,
determines addition of an additional optical fiber to accommodate
the additional optical path, and determines the additional optical
path as the optical path.
(Supplementary note 5) The optical path design apparatus according
to any one of Supplementary notes 1, 2, 3, and 4, further
comprising warning means for calculating the optical frequency band
utilization rate in the optical fibers and generating warning
information when the optical frequency band utilization rate having
been calculated exceeds a predetermined threshold value.
(Supplementary note 6) An optical node apparatus, comprising:
optical path information receiving means for receiving route
information and optical frequency band information concerning the
optical path determined by the optical path design apparatus
according to any one of Supplementary notes 1, 2, 3, 4, and 5; a
variable optical transponder configured to generate signal light by
modulating an optical carrier wave based on a client signal
included in the communication demand, and vary a center frequency
and an optical frequency band width of the signal light; switching
means for changing at least one of an input route and an output
route by the optical path, the switching means being connected to
one end of the optical fibers; and optical node control means for
controlling the switching means based on the route information, and
controlling the variable optical transponder based on the optical
frequency band information.
(Supplementary note 7) An optical path design method, comprising:
searching for a route of an optical path to accommodate a
communication demand and selecting a plurality of route candidates;
selecting a plurality of optical path candidates by allocating an
optical frequency band required to accommodate the optical path to
each of optical fibers on the plurality of route candidates; and
determining the optical path from among the plurality of optical
path candidates based on an optical frequency band utilization rate
in the optical fibers.
(Supplementary note 8) The optical path design method according to
Supplementary note 7, wherein the determining of the optical path
includes determining, as the optical path, the optical path
candidate with minimum optical frequency band utilization rate in a
maximum accommodation optical fiber in which the optical frequency
band utilization rate is maximum among the optical fibers.
(Supplementary note 9) The optical path design method according to
Supplementary note 7 or 8, wherein the determining of the optical
path includes selecting, among the optical fibers, an additional
optical path using a band-unused optical fiber with the optical
frequency band utilization rate being less than one, determining
addition of an additional optical fiber to accommodate the
additional optical path, and determining the additional optical
path as the optical path.
(Supplementary note 10) The optical path design method according to
any one of Supplementary notes 7, 8, and 9, further comprising
calculating the optical frequency band utilization rate in the
optical fibers and generating warning information when the optical
frequency band utilization rate having been calculated exceeds a
predetermined threshold value.
(Supplementary note 11) The optical path design apparatus according
to any one of Supplementary notes 1, 2, 3, 4, and 5, wherein the
optical frequency band utilization rate is calculated by using at
least one of number of optical frequency slots, number of optical
paths, and number of optical frequency slots that are continuously
arranged.
(Supplementary note 12) The optical path design apparatus according
to Supplementary note 2, wherein the optical transmission
performance includes at least one of an optical signal-to-noise
ratio, a nonlinear effect of an optical fiber, a crosstalk between
adjacent wavelength channels, and a passband narrowing effect due
to an optical band pass filter.
(Supplementary note 13) The optical path design method according to
any one of Supplementary notes 7, 8, 9, and 10, wherein the
selecting of the plurality of route candidates includes selecting
the plurality of route candidates based on optical transmission
performance using the optical fibers.
(Supplementary note 14) The optical path design method according to
Supplementary note 13, wherein the optical transmission performance
includes at least one of an optical signal-to-noise ratio, a
nonlinear effect of an optical fiber, a crosstalk between adjacent
wavelength channels, and a passband narrowing effect due to an
optical band pass filter.
(Supplementary note 15) The optical path design method according to
any one of Supplementary notes 7, 8, 9, 10, 13, and 14, wherein the
optical frequency band utilization rate is calculated by using at
least one of number of optical frequency slots, number of optical
paths, and number of optical frequency slots that are continuously
arranged.
(Supplementary note 16) A computer-readable recording medium
recording a program for making a computer function as route
candidate selection means for searching for a route of an optical
path to accommodate a communication demand and selecting a
plurality of route candidates; optical path candidate selection
means for selecting a plurality of optical path candidates by
allocating an optical frequency band required to accommodate the
optical path to each of optical fibers on the plurality of route
candidates; and optical path determination means for determining
the optical path from among the plurality of optical path
candidates based on an optical frequency band utilization rate in
the optical fibers.
While the invention has been particularly shown and described with
reference to example embodiments thereof, the invention is not
limited to these embodiments. It will be understood by those of
ordinary skill in the art that various changes in form and details
may be made therein without departing from the spirit and scope of
the present invention as defined by the claims.
REFERENCE SIGNS LIST
100, 300 Optical path design apparatus 110 Route candidate
selection section 120 Optical path candidate selection section 130
Optical path determination section 200 Optical node apparatus 210
Optical path information receiving section 220 Variable optical
transponder 230 Switching section 240 Optical node controller 340
Warning section 1000 Optical communication network 1001 to 1016
Optical node 1101 to 1105, 6101 to 6109 Optical path 1201 to 1212,
1301 to 1312, 6901 Optical fiber
* * * * *